Quickly movable elastically engaging screw-and-nut mechanism

ABSTRACT

A screw-and-nut mechanism comprises a supporting seat, one or more semi-nuts and the actuating member thereof, characterized in that the engagement of internal thread on the semi-nut with external threa on the screw is started elastically, then completed and locked by a positive element, and that the disengagement thereafter of the related elements is accomplished positively. Such a mechanism can be used in various kinds jacks, vices, sliding tables of machine tools, as well as other devices which is driven by a screw and desired to pas through its return travel quickly.

This application is a continuation-in-part of PCT internationalapplication No. PCT/CN95/00068 which has an international filing date ofAug. 18, 1995 which designated the United States, the entire contents ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a quickly movable elastically and automaticallyengaging screw-and-nut mechanism (referred to as "F nut pair" in thefollowing) which is a new type of screw-and-nut mechanism and can beused on the carriers such as a car screw jack, bench vice, architecturalscaffold, sliding table of machine tool and the like, and other meansthat require using a screw-and-nut assembly as a kinematic pair of adrive that quickly passes over an idle stroke. Also it can be used as a"means for speedly adjusting distance and locating positions" whichallows arbitrary adjustment and positioning. The key technique used is amechanically program-controlled, elastically engaging, automaticallyopening and closing screw-and-nut pair of the invention, which allowsthe semi-nuts under the effect of the mechanically programmed andautomatically controlled system to auto-matically and successivelyperform the following five predetermined mechanically program-controlledactions (referred to "5 steps for automatically opening and closing" inthe following): (1) The thread peak elastically and automaticallyaligning with the,.thread valley; (2) the thread peak and the threadvalley automatically and elastically engage with each other in "fullthread depth"; (3) rigidly selflocking the completely engaged semi-nutsand screw; (4) releasing selflocking to wait for seperating; and (5)rigidly seperating the semi-nuts and the screw.

BACKGROUND ART

Many patents relate to quickly opening and closing screw-and-nutmachanism with either the screw or the nut up-and-down typo system. Suchpatents include U.S. Pat. Nos. 4,834,355, 4,923,185, 5,282,392 and otherrelated patents such as CN 2078210U, CN 1047466A, CN2065969U,CN2057131U, CN1065514A. In these patents, the engagement of thread peaksand thread valleys of the screw and nut is essentially achieved by meansof a rigid operation actuating device in the form of a variety of cams,links etc. to directly and rigidly make forced engagement. Problemsexisted and included failure in engagement of the threads and thethreads incapable to work normally. Thus there are two drawbacks: one ofthe drawbacks is a low percentage of the number of threads engagedrelate to the total number of threads. The reason is evident. Since thethread peak of either a triangular thread or trapezoid thread both havea certain width, these thread peaks are likely to collide with eachother and not to be engaged when they are engaged in a rigid manner. Andthe probability of this phenomena happening increases as the width ofthe thread peak increases. The other drawback is a low percentage of thenumber of threads engaged in "full thread depth" in the total number ofthreads. The full thread depth is the depth between the thread peak andthread valley of the semi-nut and screw which can be engaged. In a rigidmanner, a complete engagement in "full thread depth" can be attainedonly when the center of thread peak and the center of thread valley ofthe semi-nuts and screw are just aligned with each other. It is evidentthat the probability is also certainly very low, so the most engagementsof the threads are not engagement in "full thread depth". Although theyare engaged, the engaging depth at every instance is not ideal.Sometimes it begins to work when the engagement of the internal andexternal threads have not yet reached the specified depth, which lowersloading capacity and reliability of the screw threads. Also in the priorart, there is a Patent CN 2139872Y, having an engaging means for itssemi-nuts. Although the present employs a spring for elasticallyengaging, the disengaging of its semi-nuts is accomplished by anothermanual operating lever. This patented technique belongs to a technicalfield of rather primitive, manually operating opening and closing of ascrew-and-nut pair without any mechanically programmed, automaticallycontrolled system. It does not belong to the same technical field of thepresent invention and does not have the function of performing "5 stepsfor automatically opening and closing". In summary, by using the keytechnique "mechanically program-controlled, elastically engaging,automatically opening and closing a screw-and-nut pair", the presentinvention can perform "5 steps for automatically opening and closing",to thereby overcome the various drawbacks which exist in theabovementioned reference documents.

SUMMARY OF THE INVENTION

The invention provides a quickly movable elastically engagingscrew-and-nut mechanism (referred to as "F nut pair" in the following)comprising: a screw, semi-nuts; a supporting seat; and an opening andclosing device. There is provided one or more semi-nuts uniformlydistributed around the cross-section of a screw which is supported by asupporting seat. The semi-nuts are located between the supporting seatand the up-and-down sleeve and are provided with an opening and closingmeans which can automatically rise or drop. The up-and-down sleeve isprovided with an antishift means to prevent shifting along the axialdirection of the screw. The supporting seat includes supporting arms(one or two), a supporting hole (one or two), a supporting body(including means connected to the carrier such as pivot axle O₁), anup-and-down guide member which is fitted with up-and-down slidingguideways of the semi-nuts, and a position limiting member. The screwpasses through the supporting hole, the semi-nuts and the up-and-downmeans (such as up-and-down sleeve, including axially antishift means) ina movable type of engagement. For two or more semi-nuts, they should bearranged around the center of the screw. The semi-nuts have internalthreads which extend less than a half of the periphery in addition tosliding guideways for guiding the up-and-down movement, as well as anactuative member to transmit the up-and-down force. The "mechanicallyprogram-controlled, automatically opening and closing device for thesemi-nuts" (referred to as "automatic opening and closing device" in thefollowing) which is used to control the automatic and synchronousopening and closing motion of the semi-nuts comprises an "elasticallyengaging actuating element" (such as spring) acting on th semi-nuts, a"rigid self-locking actuating element" for rigidly selflocking thesemi-nuts, and a "seperating actuating device" (such as cam profile,link mechanism) for rigidly seperating the semi-nuts. The "automaticopening and closing device" further comprises a mechnicallyprogram-controlled motion assigning actuating element (such asup-and-down sleeve), an automatic, synchronous overload seperatingdevice (such as pawl, spring hoop etc.) and an upward stroke limitingdevice, a safeguard device, and a speed changing device which permitsthe screw to advance or retract with either a quick or a slow speed.

By using a "mechanically program-controlled, elastically engaging,automatically opening and closing screw-and-nut pair", the invention hasfound a reliable, simple and practical embodiment/scheme of amechanically programmed, automatically controlled system. The scheme canmake the semi-nuts successively perform the "5 steps for automaticallyopening and closing" according to the predetermined motion procedure inan operating cycle period of one turn of the positive or inverserevolution of the screw. The concrete technical scheme of the inventionis to use an elastic means to engage the internal threads of the nut andthe external threads of the screw in a manner like a soft landing. Arigid self-locking actuating device is used for self-locking the nutafter it has been engaged. When it is desired to operate in the inverseway to facilitate the seperation between the internal and externalthreads, a rigid automatic seperating device is used. The rigid andelastic technique are used in a combined manner, which ensures not onlythe percentage of threads engaged reaching 100% but also the percentageof threads engaged in full standard depth reaching 100%. At the sametime, the screw-and-nut pair which is in engagement and under heavy loadcan ensure its reliability on self-locking.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a schematic view illustrating the work principle of a carscrew jack which employs the "F nut pair" of the invention and has thefunction to rise or drop with two speeds (quick and slow).

FIGS. 2A-2B are a main view of the first ambodiment of the "F nut pair",it has two semi-nuts, wherein an "elastically engaging actuatingelement" is a "retractable plate spring", a "rigid self-locking element"is an internal curved cam, and a "separating actuating device" is an endface cam pair which is provided on the end faces of the semi-nuts. Inthe figure, the screw 4 notates a clockwise direction (referred to as Mdirection in the following), where the internal and external threads arein an engaging state.

FIG. 3 is a similar main view as FIG. 2 but the screw 4 rotatescounterclockwise (referred to as N direction in the following), wherethe internal and external threads are in separating state.

FIG. 4A is the A--A sectional view of FIG. 2A, showing that the screw 4rotates in the M direction, the two semi-nuts make centripedal movementunder the effect of retractable plate spring, and the internal andexternal threads are in an engaging state.

FIG. 4B is the B--B sectional view of FIG. 2, showing that after thesemi-nuts have been engaged with the screw, the semi-nuts areself-locked by the internal curved cam profile.

FIG. 5A is the D--D sectional view of FIG. 3, showing that the screw 4rotates in the N direction, where the internal and external threads arein a seperating state.

FIG. 5B is the E--E sectional view of FIG. 3, showing that the semi-nutshave been released from the self-locking position and the semi-nuts havea centrifugal seperating movement under the effect of the end face campair.

FIG. 6A is a perspective view of the supporting seat of FIG. 2A.

FIG. 6B is a perspective view of the up-and-down sleeve of FIG. 2A.

FIG. 6C is a perspective view of the upper and lower two semi-nuts ofFIG. 2A.

FIG. 6D is a perspective view of the retractable plate spring of FIG.2A.

FIG. 7A is a main view of the second embodiment of the "F nut pair",wherein "elastically engaging actuating element" is a spring steel wire,the "rigid self-locking element" and the "seperating actuating element"are disc-shape cam profiles which are provided on the up-and-downsleeve. In this figure, the screw 4 rotates in M direction, the internaland external threads are in engaging state.

FIG. 7B is the F--F sectional view of FIG. 7A.

FIG. 7C is the G--G sectional view of FIG. 7A.

FIG. 8A is a main view of the third embodiment of the "F nut pair",wherein the "elastically engaging actuating element" is a compressionspring, and the self-locking and seperating device are the same as FIG.7A, but in this figure, the double speeds changing device is integralwith the paw. When the screw is in the slow speed state, when the screwcan rotate arbitraily in M or N direction, but it is in the self-lockingstate, the internal and external threads can not be seperated from eachother.

FIG. 8B is the J--J sectional view of FIG. 8A, showing that the pawl islifted away from the screw.

FIG. 8C is another J--J sectional view of FIG. 8A, showing that the pawlis lowered and inserted into the keyway of the screw 4.

FIG. 8D is the partial H--H sectional view of FIG. 8A.

FIG. 9A is a main view of the fourth embodiment of the "F nut pair",wherein the "elastically engaging element" is a compression spring, a"rigid self-locking element" is an internal curved cam pair, and a"separating actuating device" is an external curved cam pair. In thisfigure, the screw 4 rotates in the N direction, where the internal andexternal threads are in separating state.

FIG. 9B is the K--K sectional view of FIG. 9A.

FIGS. 10A-10B are a main view of the fifth embodiment of the "F nutpair", these figures are all the same as FIG. 9B except for the use of alink machanism as "seperating actuating device" which is different fromFIG. 9B. In these figures, the screw 4 rotates in the N direction, wherethe internal and external threads are in seperating state.

FIG. 11A is a main view of the sixth embodiment of the "F nut pair",where it has only one semi-nut. The "elastically actuating element" is acompression spring, the "rigid self-locking element" is an up-and-downplate, and the "seperating actuating device" is a radial cam pairprovided on the outer periphery of the semi-nut. In this figure, thescrew rotates in the M direction, where the internal and externalthreads are in an engaging state.

FIG. 11B is one of the P--P sectional views of FIG. 11A, showing thatwhen the screw 4 rotates in the M direction, the internal and externalthreads, are engaged elastically with each other, and are self-locked bythe up-and-down plate.

FIG. 11C is the another P--P sectional view of FIG. 11A, showing thatwhen the screw 4 rotates in the N direction, the internal and externalthreads separate from each other under the effect of the up-and-downplates of the cam pair.

FIG. 12A is a perspective view of the supporting seat of FIG. 11A.

FIG. 12B is a perspective view of the semi-nut of FIG. 11A.

FIG. 12C is a perspective view of the up-and-down sleeve of FIG. 11A.

FIG. 12D is a perspective view of a semi-nut with a pivot axle O₁). Thepivot axle in FIG. 11A is connected with the carrier (screw jack). Thepivot axle is modified to be provided derived from semi-nut through anequivalent transformation.

FIG. 13 is the seventh embodiment of the "F nut pair", which is on theFIG. 11A. The internal threads are provided in the supporting seat. The"elastically engaging element" is a compression spring, white theself-locking and seperating device is an eccentric cam.

FIG. 14 is the eighth embodiment of the "F nut pair", which is derivedfrom FIG. 13. The internal threads are provided in the eccentric cam,while the "elastically engaging element" is a torsion spring.

FIG. 15A is a partial main view of an overload seperating device of thesemi-nut opening and closing mechanism wherein the device is of an endface friction cone type.

FIG. 15B is the A--A sectional view of FIG. 15A.

FIG. 16A is a partial main view of an overload seperating device of thesemi-nut opening and closing mechanism wherein the device is of outwardexpandable friction ring type.

FIG. 16B is one of the B--B sectional views of FIG. 16A, showing thestructure of an outerward expandable friction ring.

FIG. 16C is the another B--B sectional view of FIG. 11A, showing thestructure of an inward expandable friction ring.

FIG. 17A is a partial main view of overload seperating device of thesemi-nut open and closing mechanism wherein the device is of axialguiding piller (or ball) type.

FIG. 17B is a partial main view of overload separating device of thesemi-nut opening and closing mechanism wherein the device is of radialball (or pillar) type.

FIG. 18 is a main view of the "F nut pair" of the invention when it isused on the practical carrier of a bench vice.

FIG. 19A is a schematic view of the embodiment of a "quick distanceadjusting and positioning means" which employs the "F nut pair" of theinvention and can be used for when arbitrary distance adjusting andsetting is required.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 2 is the first embodiment (embodiment A) of the invention. Thecarrier for use of the key part "F nut pair" is a screwjack used forreplacing a tire of a car as shown in FIG. 1. The "F nut pair" ismounted on the pivot axle O₁ at right side of the screw jack.

The screw jack comprises a bottom seat 6, top support 2, four links withsector gears, left pivot axle O₂, right pivot axle O₁, plane bearing,screw 4 with handle 1, and "F nut pair" of the invention which isintegral with the right pivot axle O₁. The left end of the screw 4 isconnected with the pivot axle O₂ and its right end threaded part ismatched with the "F nut pair". When operating, the screw 4 is rotated,by means of the "F nut pair", the distance between the left and righttwo pivot axles O₂ and O₁ is shortened or enlarged, and the top supportlifts a car up or down through the link mechanism.

FIG. 2 is the main view of the "F nut pair" of the invention, whereinthe screw 4 is rotated in the M direction with the internal and externalthreads being in the normal state of engagement. This embodiment has twosemi-nuts. The features of its opening and closing actuating mechanismare: the elastically engaging actuating element of the semi-nut is aretractable type plate spring 12; the rigid self-locking element is aninternal-currved type cam pair and the seperating actuating device is anend face cam pair provided at the end face of the semi-nut.

The concrete structure of this embodiment comprises supporting seat 13,two upper and lower semi-nuts 7 and 8, retractable plate spring 12,up-and-down sleeve 11, cam guide pin 16, pawl 10, spring hoop 9,limiting stop pin 14, clamp plate 15, speed changing device 17 and thescrew 4. As the carrier of the "F nut pair" is a screw jack, so thesupporting seat is to be connected to the pivot axle 13.1 (as FIG. 6-I).The screw 4 passes through supporting hole 13.2 and the inner hole 11.1of the up-and-down sleeve, and cooperates with the semi-nuts and their"automatically opening and closing device." The front and rear two outerside faces 7.1, 7.2, 8.1, 8.2 of the two semi-nuts 7 and 8 are inmovable fit with the inner side guideway faces 13.4, 13.5 of thesupporting seat; and the left and right two end faces 7.3, 8.3 and 7.8,8.8 are in movable fit with the right and guideway face 13.3 of thesupporting seat and the left end guideway face 11.4 of the up-and-downsleeve respectively. As to the "separating actuating device" of thesemi-nuts, this embodiment provides end face cam grooves 7.10 and 8.10on the right end face of the semi-nuts 7 and 8, which engagerespectively with cam guide pins 16A and 16B on the left end face 11.4of the up-and-down sleeve 11 to form the end face cam pair, i.e. theseperating actuating device. The design features of cam profile of theabove cam pair are as follows (take the upper semi-nut 7 as example, seeFIG. 4B and FIG. 5B): Let the radii of the internal curved profile ofthe cam be maximum (RII) at the right conner (at position II) of the camprofile,. and be minimum (RI) at the left corner (at position I), thedifference of the two radii is the amount to be moved outward by thesemi-nut 7 when it is seperated, as shown in FIG. 5A. When the cam guidepin 16A rotates with the screw 4 and the up-and-down sleeve together inthe N direction from position III, throught position II to position I,the internal threads 7.9 and 8.9 of the semi-nuts 7 and 8 seperate fromthe external threads 4.1 of the screw 4 at once. Of course, as theup-and-down sleeve 11 rotates in N direction, its self-locking internalcurved cam profile also rotates in N direction from position I toposition III for awaiting orders (see FIG. 5B). As to the elasticallyengaging actuating element of this embodiment, it is the retractableplate spring 12 rendering its slow and uniform centripedally retractingresilence to the semi-nuts softly through the curved faces 7.4 and 8.4on the groove bottom of the semi-nuts. As to the rigid self-lockingactuating element, it is the internal curved cam profiles 11.2 and 11.3provided on the up-and-down sleeve 11. Its working principle can bediscussed as follows (take the upper semi-nut 7 as example): When theup-and-down sleeve rotates in M direction, the cam guide pin 16A willmove from position I→position II→position III, thus in the up-and-downguideway, the semi-nut 7 makes centripedal elastically engaging movementin a soft landing manner under the effect of plate spring until reachingthe standard engaging depth which is specified by the thread form asshown in FIG. 4A. Meanwhile, the curved face 7.7 of the upper cam of theupper semi-nut 7 locates also at its lowest position, and the internalcurved profile 11.2 of the cam on the up-and-down sleeve 11 has justrotated to the position I, as it makes engagement rigidly with theexternal curved cam profile 7.7 of the semi-nut, whereby allowing thesemi-nut 7 hold with the screw without seperation even when the semi-nut7 is subjected to heavy load during operation, and the aim ofself-locking attained.

The torque to rotate the above up-and-down sleeve either in M or in Ndirection is generated by the screw 4, where the torque is transmittedto the up-and-down sleeve through an "automatic synchronous overloadseperating device" mounted on the up-and-down sleeve. The "overloadseperating device" comprises a pawl 10 which is mounted in a radial hole11.6 of the up-and-down sleeve (in sliding fit), a spring hoop 9 and akeyway 4.2 on the screw 4. At the lower end of the pawl there are tworamps 10.1 whese end part could be pushed by the resilence of the springhoop to press against the "outer periphery" of the screw 4 or fall intothe keyway of the screw. When the screw rotates in M direction, the sideedges 4.3 of the keyway 4.2 of the screw touch with the ramps of pawl10.1, push the pawl and up-and-down sleeve and rotate synchronously withthe up-and-down sleeve in M direction, then each actuating device on theup-and-down sleeve forces the semi-nuts 7 and 8 to make "centripedalengaging movement" until the limiting stopper 15 on the up-and-downsleeve touches with the stop pin 14 on the supporting seat 13 and therotation is stopped. Meanwhile the screw 4 still rotates in M directionso as the force exerted by the side edge 4.3 of the keyway on the pawlramp 10.1 is increased till the upward axial component of the force isgreater than the downward pressure which is exerted by the spring hoop 9on the pawl, the ramp of pawl would be squeezed out apart form thekeyway 4.3, i.e. seperating under overload, and the screw could stillratate in M direction to lift the car. On the contary, when the screwrotates in N direction, the torque would be transmitted in the same wayto the up-and-down sleeve 11 through the pawl 10, cause the up-and-downsleeve rotate with the screw 4, and through each actuating device causethe semi-nut make "centrifugal movement" to force the internal andexternal threads to the seperated (see FIG. 3), then the quick drop ofthe screw jack is realized. If it is desired that the falling speed isto be slowed, a locking device 17 could be mounted on the supportingseat 13, this device comprises an insterting pin 17.5, a spring 17.4, asocket for inserting pin 17.3, a pin axle 17.2 and an eccentic handle17.1, wherein the front and of the inserting pin 17 is an inserting pintip 17.5, which is just aligned with the locking hole 11.5 in theup-and-down sleeve 11. The working principle of the locking device is asfollows: when it is desired that the screw should have the functions ofslow retract and slow advance (i.e. the screw jack can rise or drop in aslow way); at first, operate the handle, let the screw 4 rotate in Mdirection, which causes the internal and external threads to be inengagement, then let the arrow of the eccentric handle be placed invertical direction (as shown in FIG. 2A), meanwhile the eccentric handle17.1 is at the position of short axis (i.e. the bottom face 17.7 of theeccentric handle 17.1 is in contact with the upper end face 17.6 of thespring seat 17.3), the inserting pin 17 could be inserted in the lockinghole 11.5, and the up-and-down sleeve 11 is fixed to be incapable ofrotation, thereby the internal threads of the semi-nuts 7, 8 and theexternal threads of the screw could be kept in engagement, this is thesame as conventional screw drive mechanism, and the original functionsof slow advance and alow retract are completely retained. When it isdesired that the screw should have the functions of quick advance andquick retract, the eccentric handle 17.1 could be placed with its arrowin horizontal position, whereby the eccentric handle 17.1 is at theposition of long axis (i.e. the side face of the eccentric handle 17.1is in contact with the upper end face 17.6 of the spring seat 17.3).Meanwhile the inserting pin tip 17.5 retracts from the locking hole 11.5of the up-and-down sleeve 11 and the up-and-down sleeve 11 could bebrought by the screw and pawl to rotate in N direction. Thus theinternal threads of the semi-nuts could be seperated from the externalthreads of the screw, to thereby cause the screw to have the function ofspeedly passing through an idle stroke. If the carrier to be applied isa screw jack, then the quick rise or drop of that screw jack can beattained.

FIG. 7A shows the main view of the second embodiment of the "F nutpair". In this embodiment, the equivalent transformation theory M ofrelative motion is applied, only the cam profiles of self-locking andseparating actuating elements in FIG. 2 of the first embodiment aretransferred to the same cam on the up-and-down sleeve, while others arethe same. The concrete structure is as follows: The cam guide pins 19and 20 are mounted respectively on the right side end face of thesemi-nuts 21 and 22, which are restrained to make up-and-down as well asopening and closing movements in a frame shape up-and-down guideway(such as that composed of 4 faces 23.1-23.4, see FIG. 7B, or othershapes as dovetail, cylinder etc.) of the supporting seat 23. Theelastically engaging actuating element of the two semi-nuts is a springhoop 24. The post-engagement "rigid self-locking elements" are theinternal curved faces 18.4 and 18.5 on the up-and-down sleeve 18 whichhook up the cam guide pins 19, 20 to selflock (see FIG. 7C), the"seperating actuating device" is undertaken also by an up-and-down camprofile 18.1 provided on the same up-and-down sleeve, the cam profile18.1 with its minimum radius R₁ at 18.2 and maximum radius R₂ at 18.3cooperates with the cam guide pins 19, 20 to form cam pairs for makingthe seperating motion. As to the restraint of axial shift of theup-and-down sleeve 18, it is accomplihed by providing bosses 19.1 and20.1 to the end face of cam guide pins 19, 20 for resisting against theright side face 18.6 of the cam 18. Alternatively, it can beaccomplished by mounting a large washer with cylindricaly protruded edgeor a housing to the right side end face 18.6 of the up-and-down cam 18and securing to the supporting seat 23 (such as by welding or connectingwith screw etc.) as shown in FIG. 8A. As to the working procedure ofengaging, self-locking and seperating, since it is completely the sameas the first embodiment both in operating process and in workingprinciple, it will not be further discussed.

FIG. 8A is the main view of the third embodiment of the "F nut pair".The structural form of some mechanical elements of the above secondembodiment in FIG. 7A has only made some equivalent transformationaccording to the equivalent transformation theorem, such as elasticallyengaging element is replaced by two compression springs 25, 26, whilethe axially anti-shift means of the up-and-down sleeve is replaced by aclosed dustproof housing 28 which is connected to the supporting seat 30by screw 29. Besides, the inserting pin tip 17.5 and the pawl 10 ofspeed changing means in FIG. 2 has combined into a new pawl rod 31.Other structures are the same as the second embodiment, so there willnot be discussed further. But one point may be mentioned that theseequivalent transformation of the third embodiment not only improvemanufacturability but also also enhance its reliability, especially thenew speed changing means 31 facilitates speed changing operation. Thespeed changing process is as follows: (1) changing into slow speed: letthe screw 4 rotate in M direction, and the two semi-nuts 36, 37 are inengagement with the screw 4. Meanwhile, rotate the eccentric handle 32to the horizontal position, and insert it into a positioning slot 33.1of the positioning plate 33, as shown in FIG. 8B and 8D, whereby thelower pawl working part 31.1 of the pawl rod 31 has been lifted apartfrom the keyway 4.2 of the screw 4 by the eccentric handle 32. The theup-and-down sleeve 27 is also fixed by the handle 32 such that theformer cannot rotate further, so the two semi-nuts and the screw arealways forced into mesh. This is the same as conventional nut-screwpair, so it can only work at slow speed. (2) Changing into quick speed:the only thing to do is to lift the handle 32 (apart from thepositioning slot) as shown in FIG. 8C, whereby the pawl is released. Thepawl part 31.1 can enter into the keyway 4.2 of the screw, at the timethe working condition is the same as FIG. 3, and it requires only torotate the screw 4 in N direction, where the two semi-nuts 36, 37 willsoon be seperated from each other.

FIG. 9A is the fourth embodiment of the invention, whose "opening andclosing actuating device" is derived on the basis of FIG. 2A. Theendface cam profiles 7.6 and 8.6 (see FIG. 4B) which undertake thesemi-nuts seperating actuating device have been transferred to the outercylindrical surface of the up-and-down sleeve 38 in FIG. 9A as shown at38.1 and 38.2, and the cam guide pins 39 which match with the camprofiles are connected with the semi-nuts 34 through link rods 40. Theends of curved grooves 38.3 and 38.4 provided on the up-and-down sleeve38 are used as a position limiting means for the rotation of theup-and-down sleeve. When said ends collide with the link rods 40, therotation is limited. Others such as self locking element, elasticallyengaging element and their operating process is the same as FIG. 2A, andit requires no further discussion.

FIGS. 10A, 10B, 10C are the fifth embodiment of the invention which isderived on the basis of FIG. 2 only by changing the two cam profiles8.5, 8.6, 7.5, 7.6 into two link plates 41 and 42 as in FIG. 10A for theuse of seperating actuating element, and eliminates the cam guide pin16A, 16B on the up-and-down sleeve 13 in FIG. 2. The other such as"elastically engaging actuating element" and "rigid self-lockingelement" are essentially identical. As to how the two link plates 41 and42 cause the semi-nut rigidly separating, the seperating mechanism is asfollows: take the opening and closing of the upper semi-nut 43 as anexample. There are two pivot pins 47 and 46 inserted into the link plate41, wherein 47 is provided on the up-and down sleeve 44, 45 is providedon the semi-nut 43, and the pivot pin hole of the link plate 41 whichmatches with the pivot pin 46 is an oblong groove hold 41.1. Theoperating process is as follows: when the up-and-down sleeve 45 rotateswith the pivot pin 47 in N direction, owing to the fact that the lowerend arc 41.2 of the oblong groove hole 41.4 of the link plate 41 comesinto contact with the pivot pin 46, which will bring the semi-nut 43move along the axis 43.1 to separate away. When the up-and-down sleeverotates in M direction, owing to the fact there is a corresponding spacein the upper part of the oblong groove hole 41.1 of the link plate, sothat the elastically engaging movement of the semi-nut 43 caused by thespring 48 and the selflocking of the semi-nut 43 caused by theselflocking cam profile 45.1, both are not kindered. By utilizing theprinciple of selflocking at dead angle, i.e. the link 47 cam beselflocked when the transmitting angle α=0°, the semi-nuts also can beselflocked and the selflocking cam profile can be eliminated, where whenα=0°, the upper end arc 41.3 of the elongated groove hole 41.1 is madeto just contact with the pivot pin 46 of the engaged semi-nuts and theposition is present by stop block.

FIGS. 11A, 11B, 11C are the sixth embodiment of the invention which ischaracterized in that there is only one semi-nut 50. In this embodiment,the "elastically engaging actuating element" is a compression spring 49,the "rigid selflocking actuating element" is an up-and-down plate 51.1on the up-and-down sleeve 51, and the seperating actuating device is aradial cam profile face 50.1 provided on the outer periphery of thesemi-nut 50. When the screw rotates in M direction, the internal andexternal threads are in mesh. The concrete structure is as follows: Thesemi-nut 50 has its internal threads 50.2 less than a half of theperiphery, a plain hole 50.3 with diameter greater than that of thescrew 4, and a drop portion of cam profile 50.1 on its outer periphery.The screw 4 passes successively through left end hole 52.1 of thesupporting frame 52, plain hole 50.3 of the semi-nut,hole 51.2 of theup-and-down sleeve, and right end hole 52.2 of the supporting frame. The"elastically engaging actuating element" for the semi-nut 50 is acompression spring 49. When the internal and external threads arebrought in engagement, the up-and-down plate 51.1 on the up-and-downsleeve 51 rotates after the screw 4 and the up-and-down sleeve 51 andcomes to the upmost position, where it is inserted in a sliding fitbetween an upper top face 50.4 on the outer periphery of the semi-nut 50and an upper bottom face 52.3 of the inner cavity of the supportingframe 52, thereby achieving rigid selflocking. When the screw 4 rotatesin N direction (see FIG. 11C), the up-and-down sleeve 51 is brought torotate together through the pawl 10, and the cam pair compased by theinner side face 51.3 of the up-and-down plate and the cam profile 50.1on the outer periphery of the semi-nut 50 forces the semi-nut 50 upward,thus to separate the internal and external threads 50.3 and 4.1, untilthe inner side face 51.3 of the up-and-down plate collides with thelower plane 50.6 of.the semi-nut 50. The above device has many ways tocarry on equivalent transformation, such as the cam profile can beprovided on the inner side face 51.3 of the up-and-down plate 51.1 ofthe up-and-down sleeve; again, the pivot axle O₁ joined with the carrier(screw jack) can be transferred to the semi-nut, as shown in FIG. 12D.

FIG. 13A is the seventh embodiment of the invention, which is derived onthe basis of FIG. 11A by transferring the internal threads into thesupporting seat. It is characterized in that the supporting seat is aframe with a rectangular opening at its center. Internal threads 55.3,55.4 which are less than a half of the periphery and plain holes 55.1,55.2 with diameter greater than that of the screw 4 are provided in theleft and right two side walls of the frame of supporting seat 55. Thereare further mounted guide groove means 59, 60 (it can be mounted also onthe carrier) which allow the screw 4 to move in up-and-down directiononly. And an eccentric cam sleeve is mounted in movable fit between theupper and lower faces of the rectangular opening of supporting seat 55.On the eccentric cam sleeve, there retains only the drop portion of camprofile (rise portion of cam profile is omitted to avoid interferringwith the engaging action of the compression spring 56). The screw 4successively passes through the respective holes according to FIG. 13A.In this embodiment, the "elastically engaging actuating element" iscomposed of a guided positioning rod 57, a compression spring 56 and ahalf circular curved cushion which has a half circular arc 61.1conforming to the outer circumference of the screw, whose function is totransmit the compression force of the spring to the up-and-down movingscrew 4. The selflocking and seperating actuating devices are realizedby an overload seperating means (as pawl 10) and a cam pair which iscomposed of an eccentric cam sleeve and the upper and lower parallelplanes 55.5 and 55.6 of the rectangular opening of supporting seat 55.

FIG. 14A is the eighth embodiment of the invention which is acombination of FIG. 11A and FIG. 13A. The internal threads are directlyprovided in the curved face of inner cavity of the eccentric cam sleeve63, the structure of said inner cavity 63.1 is the same as the innercavity of the semi-nut 50 in FIG. 11A. The outer structure of theeccentric cam sleeve 63 and the rectangular opening of the supportingseat 62 are also essentially the same as FIG. 13A. This embodiment ischaracterized in that, the internal threads 63.2 of the eccentric camsleeve 63 and the external threads 4.1 of the screw 4 are engaged alonga direction tangent to the outer circunference of the screw (while inall the previous embodiments, the engagement proceeds along a radialdirection), so the "elastically engaging actuating element" used is atorsion spring, whose one end 65.1 is connected with the eccentric camsleeve 63 and the other end 65.2 is connected with the supporting seat62. Pawl 67 used as overload separating, means is directly provided onthe eccantric cam sleeve 63.

Summarizing the above, for the "F nut pair" of the invention, manyequivalent mechanisms can be used to replace these embodiments. Forinstance, an Archimede's spiral and face threads commonly used in thethree-jaw automatically centering chuck of a lathe can be used toreplace the end face cam mechanism in FIG. 2A; again, the number ofsemi-nut can be one or two, or more than two. All these are within thescope of the invention.

With respect to the "automatic, synchronous overload seperating device"used in the invention, besides the overload separating device of FIG. 2Awhich is composed of a pawl 10 and a spring hoop 9, there are a greatmany of other equivalent overload seperating devices. As to the form, itmay be of single direction or of double direction, as to the drivemanner, it may be electro-magnetic, hydraulic or pneumatic, as to theoverload separating element, various elements such as pawl (of single ordouble direction), teeth, ball, guide pillar, friction cone (disc,plate, block, cushion) and various elastic elements (such as spring,elastically expandable loop or ring, expandable sleeve) can be used. Inthe following, some of the equivalent overload separating devicesderived from FIG. 2 are listed.

FIG. 15A, 15B show a friction overload separating device using afriction ring(or friction cone). Its working principle is as follows: Afriction ring (cone) 121 is mounted in an up-and-down sleeve 3A, andslidably encloses the outer circumference of the screw 4. Friction face(cone) 121 tightly presses against the right friction face (cone) 3A.10of the up-and-down sleeve 3A under the effect of the compression spring122, friction ring (cone) 121 is connected to the screw 4 through aguide key 123. When the screw 4 rotates, its driving torque istransmitted through keyway 4.1, guide key 123, friction face of frictionring (cone) 121.1 to the up-and-down sleeve 3A which is brought torotate together, until it stops when colliding with an upward strokelimiting means, but the screw will continue to rotate. Meanwhile thisfriction pair is overloaded and slides over each other without hinderingthe rotation of the screw, and the screw can achieve its predeterminedjob. The above stated contact faces 121.1 and 3A.10 of the friction ring(cone) can be replaced by a pair of teeth which can slide over eachother under the effect of a compression spring 122 when overload occurs.Of course the amount of compression deformation of the compressionspring must be greater than the depth that the teeth would be insertedin.

FIGS. 16A and 16B is an overload separating device of an expandable ringwith its outer circumference as a friction surface. This embodiment usesan outer circumference friction expandable ring 125 in FIG. 16A toreplace the friction ring 121 and compression spring 122, the expandablering is still kept by a check ring 124, and there is an axial open slot125.1 provided on the cylindrical body of the expandable ring 125. Whenthe expandable ring is in the free state, its outside diameter 125.2 isgreater than the inside diameter of inner hole 3A.11 of the up-and-downsleeve 3A. When assembling, the open slot 125.1 is forced to contract,it releases after the expandable ring is inserted into the inner hole3A.11, thus by resilence the outer circumference 125.2 of the expandablering 125 expands and sticks on the inner wall of the inner hole 3A.11 ofthe up-and-down sleeve, and results a certain amount of frictionalforce. The inside diameter of the expandable ring is slightly greaterthan the outside diameter of the screw, and the former is connected tothe latter through a guide key 123. Its operating process is the same asthe type of friction ring in FIG. 15A, the only difference is that thefriction surface which can slide over at overload is transferred fromthe end face (or cone face) to the outer circumference of the expandablering.

FIG. 16C is an overload seperating device of the type of an expandablering with its inner hole as friction surface. Its working principle isessentially the same as FIG. 16B. Its expandable ring 126 has also anaxial open slot 126.1. When in free state, the inside diameter of itsinner hole is slightly smaller than the outside diameter 4.9 of thescrew 4. After the screw is inserted in the inner hole, by resilence theinner hole embraces around the outer periphery of the cylinder of thescrew 4 and results in a certain amount of frictional force (there is nokeyway on the screw). The outside diameter of the inwardly expandablering 126 is slightly smaller than the inside diameter of the inner holeof the up-and-down sleeve 3A, the driving torque of the screw istransmitted through a transmitting pin 127 to the up-and-down sleeve 3A.The operating process is the same as FIG. 16B, but that the frictionsurface which can slide at overload is directly undertaken by thefriction surface lying between the outer circumference of the screw 4and the inner hole of the expandable ring.

FIG. 17A is an overload seperating device of the type of axiallydistributed guide pillar (or steel bar). Its working principle in asfollows: On the left end face of a sliding sleeve 128 which enclosesaround the screw 4, there are radial small holes, small compressionsprings 129 and a guide pillar 130 (or steel ball) are fitted into thesmall holes, and engages with the resistant small cone pits 3A.12 whichare provided on the right end face of the up-and-down sleeve 3A. Theoperating process is essentially the same as FIG. 15A, the onlydifference is that, the pure end face friction in FIG. 15A is changedinto small cone pit resisting with guide piller (or steel ball) in FIG.17A. The device shown in FIG. 17B is the equivalent mechanical structureof that shown in FIG. 17-I, where the axially arranged holes of guidepillar in FIG. 17A have been changed into radially arranged holes inFIG. 17B where 3A.13 represents an axially resistant groove.

Summarizing the above, although the carrier related is a screw jackwhich can quickly or slowly up or down, but the most essential nucleusof the invention is a "F nut pair". That mechanism has a wide varietyuses an applied carrier. If the applied carrier is a screw jack, thenthat screw jack is a "double speed screw jack". If the applied carrieris a bench vice, then the invention is a quickly or slowly, opening orclosing bench vice. For instance, FIG. 18 is the embodiment which usesthe "F nut pair" as shown in FIG. 2A, but the carrier is changed from ascrew jack to a bence vice. The method of retrofitting really is verysimple. One needs only to change the connecting part between therespective carrier and the "F nut pair". For example the pivot axle O₁on the supporting seat 1A in FIG. 2 is omitted, and the bottom plane1A'1 and vertical plane 1A'2 on the supporting seat 1A' are utilized todirectly contact with the corresponding positioning planes a₁ and a₂ onthe fixed body "a" of the bench vice, and the screws "h" are used forfastening. While the screw 4 needs only to connect with the movable bodyof the bench vice, others remain unchanged. Furthermore, it is possibleto derive many other devices which may be used for other purposes. Forexample FIG. 19A is derived from FIG. 11A by changing pawl 10 into aguide key 70, while the speed-changing device 17 is omitted and adding astop block 74.1 on the left outer periphery of the up-and-down sleeve isadded. Adding a positioning block 71 on the supporting seat 72, andchanging over the connecting manner between the supporting seat and thecarrier is necessary, while other structures remain the same as FIG. 2A.Thus FIG. 19A becomes a quick positioning device which employs the "Fnut pair". The positioning device can be used in at least two methods ofapplication: One of which is to fix the supporting seat, let the screwmove in axial direction at will. When it is positioned, rotate the screw73 in M direction about one turn, so the position can be locked soon.The invention can be used in a quick bench vice, where it needs onlyadding a drive screw at the rear end of the screw to apply a clampingforce; the other method is to fix the screw, where in that case, thesupporting seat must rotate inversely in N direction about one turn,then it can move at will. When the screw reaches the desired position,the screw further rotates in M direction about one turn, so that thesupporting seat can be locked at a certain position on the screw 73. Theinvention can be used in rigid stroke stop block where the axial forceis considerably large and the axial position are frequently required toadjust.

As a summary, the applied carrier of the "F nut pair" of the invention,besides in the screw jack, it can be used further in: a bench vice, amachine vice, a pipe vice, a sliding table of a machine tool, atailstock of a lathe, an architectural scaffold whose height can beadjusted. All of the aforementioned embodiments are within the scope ofthe invention. It needs only using some common methods to change theconnection with the above applied carrier.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art wereintended to be included within the scope of the following claims.

We claim:
 1. An elastically engaging screw-and-nut mechanismcomprising:a screw; a first semi-nut with threads; a second semi-nutwith threads; a supporting seat including support arms, a positionlimiting member, a support hole, a supporting body, and guidewaysdisposed between said support arms; a sleeve, said first and secondsemi-nuts being disposed between said sleeve and said supporting seat,said semi-nuts contacting said guideways of said supporting seat; ascrew being supported by said supporting seat and disposed within saidsupport hole and being enclosed by said sleeve and said semi-nuts; anantishift device for preventing shifting of said sleeve along an axialdirection of said screw; an elastically engaging actuating element whichengages with said semi-nuts; a rigid self-locking actuating element forrigidly locking said semi-nuts; a separating actuating device disposedon each semi-nut for separating said first and second semi-nuts; and anoverload separating device whereby when said separating actuatingdevices separate said semi-nuts, said screw moves at a first speed in atranslational manner past said semi-nuts, and when said rigidself-locking actuating element locks said semi-nuts, said screw moves ata second speed in a rotative manner past said semi-nuts, said firstspeed being substantially greater than said second speed, saidengagement between said semi-nuts and said screw is in an elasticmanner, said locking of said semi-nuts is in a rigid manner, and saidseparating of said semi-nuts-and said screw is in a rigid manner.
 2. Thescrew-and-nut mechanism of claim 1, wherein each semi-nut includes anouter curved groove, said separating actuating device includes end facecam grooves, said sleeve further includes guide pins, said end face camgrooves engage with said guide pins, said elastically engaging actuatingelement includes a retractable plate spring contacting each outer curvedgroove of a respective semi-nut, and said rigid self-locking actuatingelement includes curved cam profiles disposed on said sleeve.
 3. Thescrew-and-nut mechanism of claim 1, further comprising a speed changingdevice which alters the speed at which said screw moves past saidsemi-nuts, said speed changing device includes a supporting seat, alocking device, said locking device further includes an inserting pin, aspring, and a handle, said inserting pin engaging a locking hole in saidsleeve in a first position, and being spaced apart from said lockinghole in a second position.